1. Field of the Invention
The invention relates to a process for preparing amino-alkylsilanes.
2. Description of the Related Art
Aminoalkylsilanes can, by way of example, be used as precursors for preparation of aminoalkyl-terminated polysiloxanes. They are also used as adhesion promoters.
DE 100 49 183 C1 and US 2003/0130543 A1 mention cyclic silazanes of the general formula (I) which are prepared via amination of chloroalkylsilanes
where                R is a divalent Si—C— and Si—N-bonded, if appropriate cyano-or halogen-substituted, C3-C15-hydro-carbon radical in which one or more nonadjacent methylene units are optionally replaced by groups —O—, —CO—, —COO—,—OCO—, or —OCOO—, —S—, or —NRx—, and in which one or more nonadjacent methyne units are optionally replaced by groups —N═, —N═N—, or —P═, where at least 3 and at most 6 atoms are present between the ring silicon and nitrogen atoms,        Rx is hydrogen or a C1-C10-hydrocarbon radical, if appropriate halogen-substituted, and        R2 is a hydrogen atom or a monovalent, if appropriate cyano- or halogen-substituted, Si—C—bonded C1-C20-hydrocarbon radical or C1-C20-oxyhydrocarbon radical, in which, in each case, one or more nonadjacent methylene units are optionally replaced by groups —O—, —CO—, —COO—, —OCO—, or —OCOO—, —S—, or —NRx—, and in which one or more nonadjacent methyne units are optionally replaced by groups —N═, —N═N—, or —P═.        
If the compounds of the general formula (I) are then hydrolyzed, the product is high yields of bisaminoalkyl-substituted disiloxanes of the general formula (II) practically free from byproduct:

The particular advantage of the process described in DE 100 49 183 C1 and US 2003/0 130543 A1 is that highly reactive aminoalkylsilanes can be prepared cost-effectively from chloroalkylsilanes which have relatively good commercial availability.
However, a disadvantage of the process described in DE 10049 183 C1 and US 2003/0130543 A1 is that the reaction of the chioroalkylsilane precursor with ammonia does not give the desired product quantitatively, but instead gives secondary aminoalkylsilanes (IV) inter alia via a side reaction.

These are then practically impossible to remove by distillation from the bottom product of distillation of the actual principal product, because their boiling point is extremely high, but they sometimes still comprise fractions which have the desired primary aminoalkyl function. It is moreover also technically difficult to achieve complete isolation of the target product of the general formula (I) present in the bottom product of distillation, as the bottom product becomes ever more viscous during the distillation process. Accordingly, a proportion (I) likewise remains in the bottom product of distillation. This product then has to be sent for expensive disposal.